The PHANGS–MUSE nebular catalogue Groves, B; Kreckel, K; Santoro, F ...
Monthly Notices of the Royal Astronomical Society,
02/2023, Volume:
520, Issue:
4
Journal Article
Peer reviewed
Open access
ABSTRACT
Ionized nebulae provide critical insights into the conditions of the interstellar medium (ISM). Their bright emission lines enable the measurement of physical properties, such as the ...gas-phase metallicity, across galaxy discs and in distant galaxies. The PHANGS–MUSE survey has produced optical spectroscopic coverage of the central star-forming discs of 19 nearby main-sequence galaxies. Here, we use the $\rm {H}\,\alpha$ morphology from this data to identify 30 790 distinct nebulae, finding thousands of nebulae per galaxy. For each nebula, we extract emission line fluxes and, using diagnostic line ratios, identify the dominant excitation mechanism. A total of 23 244 nebulae (75 per cent) are classified as H ii regions. The dust attenuation of every nebulae is characterized via the Balmer decrement and we use existing environmental masks to identify their large-scale galactic environment (centre, bar, arm, interarm, and disc). Using strong-line prescriptions, we measure the gas-phase oxygen abundances (metallicity) and ionization parameter for all H ii regions. With this new catalogue, we measure the radial metallicity gradients and explore second-order metallicity variations within each galaxy. By quantifying the global scatter in metallicity per galaxy, we find a weak negative correlation with global star formation rate and stronger negative correlation with global gas velocity dispersion (in both ionized and molecular gas). With this paper we release the full catalogue of strong line fluxes and derived properties, providing a rich data base for a broad variety of ISM studies.
Context Radio continuum surveys of the Galactic plane can find and characterize H II regions, supernova remnants (SNRs), planetary nebulae (PNe), and extragalactic sources. A number of surveys at ...high angular resolution (≤25″) at different wavelengths exist to study the interstellar medium (ISM), but no comparable high-resolution and high-sensitivity survey exists at long radio wavelengths around 21 cm. Aims. Our goal is to investigate the 21 cm radio continuum emission in the northern Galactic plane at < 25″ resolution. Methods We observed a large percentage of the Galactic plane in the first quadrant of the Milky Way (l = 14.0−67.4° and |b| ≤ 1.25°) with the Karl G. Jansky Very Large Array (VLA) in the C-configuration covering six continuum spectral windows (SPW). These data provide a detailed view on the compact as well as extended radio emission of our Galaxy and thousands of extragalactic background sources. Results We used the BLOBCAT software and extracted 10 916 sources. After removing spurious source detections caused by the side lobes of the synthesized beam, we classified 10 387 sources as reliable detections. We smoothed the images to a common resolution of 25″ and extracted the peak flux density of each source in each SPW to determine the spectral indices α (assuming I(ν) ∝ να). By cross-matching with catalogs of H II regions, SNRs, PNe, and pulsars, we found radio counterparts for 840 H II regions, 52 SNRs, 164 PNe, and 38 pulsars. We found 79 continuum sources that are associated with X-ray sources. We identified 699 ultra-steep spectral sources (α < −1.3) that could be high-redshift galaxies. About 9000 of the sources we extracted are not classified specifically, but based on their spatial and spectral distribution, a large percentage of these are likely to be extragalactic background sources. More than 7750 sources do not have counterparts in the SIMBAD database and more than 3760 sources do not have counterparts in the NED database. Conclusions Studying the long wavelengths centimeter continuum emission and the associated spectral indices allows us to characaterize a large percentage of Galactic and extragalactic radio sources in the area of the northern inner Milky Way. This database will be extremely useful for future studies of a diverse set of astrophysical objects.
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Molecular clouds form from the atomic phase of the interstellar medium. However, characterizing the transition between the atomic and the molecular interstellar medium (ISM) is a complex ...observational task. Here we address cloud formation processes by combining H
I
self absorption (HISA) with molecular line data. Column density probability density functions (N-PDFs) are a common tool for examining molecular clouds. One scenario proposed by numerical simulations is that the N-PDF evolves from a log-normal shape at early times to a power-law-like shape at later times. To date, investigations of N-PDFs have been mostly limited to the molecular component of the cloud. In this paper, we study the cold atomic component of the giant molecular filament GMF38.1-32.4a (GMF38a, distance = 3.4 kpc, length ~ 230 pc), calculate its N-PDFs, and study its kinematics. We identify an extended HISA feature, which is partly correlated with the
13
CO emission. The peak velocities of the HISA and
13
CO observations agree well on the eastern side of the filament, whereas a velocity offset of approximately 4 km s
−1
is found on the western side. The sonic Mach number we derive from the linewidth measurements shows that a large fraction of the HISA, which is ascribed to the cold neutral medium (CNM), is at subsonic and transonic velocities. The column density of the CNM part is on the order of 10
20
to 10
21
cm
−2
. The column density of molecular hydrogen, traced by
13
CO, is an order of magnitude higher. The N-PDFs from HISA (CNM), H
I
emission (the warm and cold neutral medium), and
13
CO (molecular component) are well described by log-normal functions, which is in agreement with turbulent motions being the main driver of cloud dynamics. The N-PDF of the molecular component also shows a power law in the high column-density region, indicating self-gravity. We suggest that we are witnessing two different evolutionary stages within the filament. The eastern subregion seems to be forming a molecular cloud out of the atomic gas, whereas the western subregion already shows high column density peaks, active star formation, and evidence of related feedback processes.
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We present SOFIA/FIFI-LS observations of the C ii 158 m cooling line across the nearby spiral galaxy NGC 6946. We combine these with UV, IR, CO, and H i data to compare C ii emission to dust ...properties, star formation rate (SFR), H2, and H i at 560 pc scales via stacking by environment (spiral arms, interarm, and center), radial profiles, and individual, beam-sized measurements. We attribute 73% of the C ii luminosity to arms, and 19% and 8% to the center and interarm region, respectively. C ii/TIR, C ii/CO, and C ii/PAH radial profiles are largely constant, but rise at large radii ( 8 kpc) and drop in the center ("C ii deficit"). This increase at large radii and the observed decline with the 70 m/100 m dust color are likely driven by radiation field hardness. We find a near proportional C ii-SFR scaling relation for beam-sized regions, though the exact scaling depends on methodology. C ii also becomes increasingly luminous relative to CO at low SFR (interarm or large radii), likely indicating more efficient photodissociation of CO and emphasizing the importance of C ii as an H2 and SFR tracer in such regimes. Finally, based on the observed C ii and CO radial profiles and different models, we find CO to increase with radius, in line with the observed metallicity gradient. The low CO (galaxy average 2 M pc−2 (K km s−1)−1) and low C ii/CO ratios (∼400 on average) imply little CO-dark gas across NGC 6946, in contrast to estimates in the Milky Way.
Abstract
This study uses H
i
image data from the Widefield ASKAP L-band Legacy All-sky Blind surveY (WALLABY) pilot survey with the Australian Square Kilometre Array Pathfinder (ASKAP) telescope, ...covering the Hydra cluster out to 2.5
r
200
. We present the projected phase–space distribution of H
i
-detected galaxies in Hydra, and identify that nearly two-thirds of the galaxies within
1.25
r
200
may be in the early stages of ram pressure stripping. More than half of these may be only weakly stripped, with the ratio of strippable H
i
(i.e., where the galactic restoring force is lower than the ram pressure in the disk) mass fraction (over total H
i
mass) distributed uniformly below 90%. Consequently, the H
i
mass is expected to decrease by only a few 0.1 dex after the currently strippable portion of H
i
in these systems has been stripped. A more detailed look at the subset of galaxies that are spatially resolved by WALLABY observations shows that, while it typically takes less than 200 Myr for ram pressure stripping to remove the currently strippable portion of H
i
, it may take more than 600 Myr to significantly change the total H
i
mass. Our results provide new clues to understanding the different rates of H
i
depletion and star formation quenching in cluster galaxies.
Context.
Recent surveys of the Galactic plane in the dust continuum and CO emission lines reveal that large (≳50 pc) and massive (≳10
5
M
⊙
) filaments, know as giant molecular filaments (GMFs), may ...be linked to Galactic dynamics and trace the mid-plane of the gravitational potential in the Milky Way. Yet our physical understanding of GMFs is still poor.
Aims.
We investigate the dense gas properties of one GMF, with the ultimate goal of connecting these dense gas tracers with star formation processes in the GMF.
Methods.
We imaged one entire GMF located at
l
~ 52–54° longitude, GMF54 (~68 pc long), in the empirical dense gas tracers using the HCN(1–0), HNC(1–0), and HCO
+
(1–0) lines, and their
13
C isotopologue transitions, as well as the N
2
H
+
(1–0) line. We studied the dense gas distribution, the column density probability density functions (N-PDFs), and the line ratios within the GMF.
Results.
The dense gas molecular transitions follow the extended structure of the filament with area filling factors between 0.06 and 0.28 with respect to
13
CO(1–0). We constructed the N-PDFs of H
2
for each of the dense gas tracers based on their column densities and assumed uniform abundance. The N-PDFs of the dense gas tracers appear curved in log–log representation, and the HCO
+
N-PDF has the flattest power-law slope index. Studying the N-PDFs for sub-regions of GMF54, we found an evolutionary trend in the N-PDFs that high-mass star-forming and photon-dominated regions have flatter power-law indices. The integrated intensity ratios of the molecular lines in GMF54 are comparable to those in nearby galaxies. In particular, the N
2
H
+
/
13
CO ratio, which traces the dense gas fraction, has similar values in GMF54 and all nearby galaxies except Ultraluminous Infrared Galaxies.
Conclusions.
As the largest coherent cold gaseous structure in our Milky Way, GMFs, are outstanding candidates for connecting studies of star formation on Galactic and extragalactic scales. By analyzing a complete map of the dense gas in a GMF we have found that: (1) the dense gas N-PDFs appear flatter in more evolved regions and steeper in younger regions, and (2) its integrated dense gas intensity ratios are similar to those of nearby galaxies.
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Tidal dwarf galaxies (TDGs) are gravitationally bound condensations of gas and stars that formed during galaxy interactions. Here we present multi-configuration ALMA observations of J1023+1952, a TDG ...in the interacting system Arp 94, where we resolved CO(2–1) emission down to giant molecular clouds (GMCs) at 0.64″∼45 pc resolution. We find a remarkably high fraction of extended molecular emission (∼80−90%), which is filtered out by the interferometer and likely traces diffuse gas. We detect 111 GMCs that give a similar mass spectrum as those in the Milky Way and other nearby galaxies (a truncated power law with a slope of −1.76 ± 0.13). We also study Larson’s laws over the available dynamic range of GMC properties (∼2 dex in mass and ∼1 dex in size): GMCs follow the size-mass relation of the Milky Way, but their velocity dispersion is higher such that the size-linewidth and virial relations appear super-linear, deviating from the canonical values. The global molecular-to-atomic gas ratio is very high (∼1) while the CO(2–1)/CO(1–0) ratio is quite low (∼0.5), and both quantities vary from north to south. Star formation predominantly takes place in the south of the TDG, where we observe projected offsets between GMCs and young stellar clusters ranging from ∼50 pc to ∼200 pc; the largest offsets correspond to the oldest knots, as seen in other galaxies. In the quiescent north, we find more molecular clouds and a higher molecular-to-atomic gas ratio (∼1.5); atomic and diffuse molecular gas also have a higher velocity dispersion there. Overall, the organisation of the molecular interstellar medium in this TDG is quite different from other types of galaxies on large scales, but the properties of GMCs seem fairly similar, pointing to near universality of the star-formation process on small scales.
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ABSTRACT
The current generation of (sub)mm-telescopes has allowed molecular line emission to become a major tool for studying the physical, kinematic, and chemical properties of extragalactic ...systems, yet exploiting these observations requires a detailed understanding of where emission lines originate within the Milky Way. In this paper, we present 60 arcsec (∼3 pc) resolution observations of many 3 mm band molecular lines across a large map of the W49 massive star-forming region (∼100 pc × 100 pc at 11 kpc), which were taken as part of the ‘LEGO’ IRAM-30m large project. We find that the spatial extent or brightness of the molecular line transitions are not well correlated with their critical densities, highlighting abundance and optical depth must be considered when estimating line emission characteristics. We explore how the total emission and emission efficiency (i.e. line brightness per H2 column density) of the line emission vary as a function of molecular hydrogen column density and dust temperature. We find that there is not a single region of this parameter space responsible for the brightest and most efficiently emitting gas for all species. For example, we find that the HCN transition shows high emission efficiency at high column density (1022 cm−2) and moderate temperatures (35 K), whilst e.g. N2H+ emits most efficiently towards lower temperatures (1022 cm−2; <20 K). We determine $X_{\mathrm{CO} (1-0)} \sim 0.3 \times 10^{20} \, \mathrm{cm^{-2}\, (K\, km\, s^{-1})^{-1}}$, and $\alpha _{\mathrm{HCN} (1-0)} \sim 30\, \mathrm{M_\odot \, (K\, km\, s^{-1}\, pc^2)^{-1}}$, which both differ significantly from the commonly adopted values. In all, these results suggest caution should be taken when interpreting molecular line emission.
Abstract
We use PHANGS–James Webb Space Telescope (JWST) data to identify and classify 1271 compact 21
μ
m sources in four nearby galaxies using MIRI F2100W data. We identify sources using a ...dendrogram-based algorithm, and we measure the background-subtracted flux densities for JWST bands from 2 to 21
μ
m. Using the spectral energy distribution (SED) in JWST and HST bands plus ALMA and MUSE/VLT observations, we classify the sources by eye. Then we use this classification to define regions in color–color space and so establish a quantitative framework for classifying sources. We identify 1085 sources as belonging to the ISM of the target galaxies with the remainder being dusty stars or background galaxies. These 21
μ
m sources are strongly spatially associated with H
ii
regions (>92% of sources), while 74% of the sources are coincident with a stellar association defined in the HST data. Using SED fitting, we find that the stellar masses of the 21
μ
m sources span a range of 10
2
–10
4
M
⊙
with mass-weighted ages down to 2 Myr. There is a tight correlation between attenuation-corrected H
α
and 21
μ
m luminosity for
L
ν
,F2100W
> 10
19
W Hz
−1
. Young embedded source candidates selected at 21
μ
m are found below this threshold and have
M
⋆
< 10
3
M
⊙
.
Abstract
We study the tidal interaction of galaxies in the Eridanus supergroup, using H
i
data from the pre-pilot survey of the Widefield ASKAP
L
-band Legacy All-sky Blind surveY. We obtain optical ...photometric measurements and quantify the strength of tidal perturbation using a tidal parameter
S
sum
. For low-mass galaxies of
M
*
≲ 10
9
M
⊙
, we find a dependence of decreasing H
i
to optical disk size ratio with increasing
S
sum
, but no dependence of H
i
spectral line asymmetry with
S
sum
. This is consistent with the behavior expected under tidal stripping. We confirm that the color profile shape and color gradient depend on the stellar mass, but there is an additional correlation of low-mass galaxies having their color gradients within 2
R
50
increasing with higher
S
sum
. For these low-mass galaxies, the dependence of color gradients on
S
sum
is driven by the color becoming progressively redder in the inner disk when tidal perturbations are stronger. For high-mass galaxies, there is no dependence of color gradients on
S
sum
, and we find a marginal reddening throughout the disks with increasing
S
sum
. Our result highlights tidal interaction as an important environmental effect in producing the faint end of the star formation suppressed sequence in galaxy groups.
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